This invention relates to a method and apparatus for bending or curving wood materials, and in particular to a method and apparatus wherein wood material is inserted into the shaping channel of a bending template to form a curved shape.
Wood materials curved in two or three dimensions are used in industrial products of luxurious design. For example, wood materials curved in various shapes are used for furniture such as chairs, religious altars and decorations, door handles, automotive parts such as steering wheels, home electronics, and many types of nursing care equipment.
The method shown in FIG. 1 has been developed as a method of bending wood materials. In this method, wood material W is made to follow the surface contour of a bending template 21 to form a curved shape. Since this method stretches the top surface of the wood material W being curved, it has the drawback that the wood material is easily cracked. This is because the maximum tolerance for stretching wood material W in the direction of the grain is extremely small at only 1% to 2%. Wood materials have a large tolerance for compression in the direction of the grain, on the order of 30%, but with respect to stretching, they are readily disposed to tension fracture. When wood material compression in the direction of the grain exceeds maximum compression tolerance, there is a strong possibility of local cracking and splitting resulting in buckling.
The methods shown in FIGS. 2 and 3 were developed to eliminate the drawback of the method of FIG. 1. In the method shown in FIGS. 2, steel bands 22 are disposed at the outer surface of the wood material W to be shaped. In this configuration, the outer surface of the wood material W is restrained from stretching while an inner template 24 presses down between a pair of rollers 23 to bend the wood material W. In the method of FIG. 3, wood material W is sandwiched between a male template 26 and a female template 25 to produce a curved shape.
However, methods such as those shown in the figures have the following drawbacks.    (1) The surface of the wood material in contact with the steel bands must be planar. This puts restrictions on the cross-sectional shape of wood material to be shaped. For example, cylindrical wood material cannot be processed to produce a curved shape.    (2) The steel bands must curve with the wood material. Since the steel bands are required to have flexibility allowing them to bend, they cannot be made any thicker than necessary. Consequently, the steel bands can stretch during bending and result in the unfortunate case of breaking the wood material. If thicker steel bands are used to avoid stretching, they cannot bend with the wood material to produce a curved shape.    (3) It is extremely difficult to reliably hold the wood material and steel bands firmly together with no shifting. Both ends of the steel bands are in contact with wood material, but the contact regions can be damaged during bending making it easy for the wood material and steel bands to shift. If the steel bands shift and do not firmly hold the wood material, the steel bands cannot limit stretching of the wood material during bending and can be the cause of cracking.    (4) Since steel bands follow the contour of the wood material keeping it from stretching, the wood material cannot bend in three dimensions and the shapes that can be produced are limited. Therefore, bending to efficiently produce various shapes is not possible.    (5) Since wood material processing is one piece at a time, bending cannot be performed efficiently in a continuous fashion. Therefore, processing cost is high and inexpensive production in quantity is difficult.
For the previous reasons, related art methods of bending wood materials are remarkably limited in the freedom to produce various shapes, and with respect to production efficiency, industrial production in quantity is difficult. For fine wooden items such as chairs, the state of the art is manufacture by hand crafting.
The present invention was developed to eliminate related art drawbacks. Thus it is a primary object of the present invention to provide a method of bending wood materials and an apparatus for bending wood materials wherein the wood material for bending is not restricted planar material, wood material of various cross-sectional shapes can be processed into various curved shapes, breaking can be effectively prevented by bending wood material while accurately controlling its stretching, and in addition, wood material can be processed into curved shapes extremely efficiently, inexpensively, and in quantity.
The above and further objects and features of the invention will more fully be apparent from the following detailed description with accompanying drawings.